Firewood Cord Calculator (Stack Size, Price & Heat Value)

Measures a firewood stack in cubic feet and cords, shows what you paid per full cord, and estimates heat content by species along with cost per million BTU.

You can compare against your own electricity, propane and natural gas prices.

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Results will appear here once you enter your values.

How the numbers are calculated

Stack volume is length x height x depth in feet. Cords equal volume divided by 128. Wood heat is cords times the species MMBtu per cord, and usable heat multiplies that by stove efficiency.

The defaults are a stack 8 ft long, 4 ft high and 1.33 ft deep, red oak, $120 paid and a 70% stove. Volume is 42.56 cubic feet, or 0.3325 of a cord. The price works out to $360.90 per full cord. Gross heat is 8.18 MMBtu, so wood costs $14.67 per MMBtu. Usable heat at 70% is 5.73 MMBtu, or $20.96 per usable MMBtu.

For comparison, electricity at $0.16 per kWh is $46.89 per MMBtu, and propane at $3.00 per gallon is $32.80 per MMBtu. Both are before heater efficiency, which for an electric resistance heater is close to 100%.

  • Measure: stack neatly so pieces lie parallel with few gaps.
  • Stack mode limits: each dimension from 0.01 to 10,000 ft.
  • Stove efficiency: 1 to 100%.

Limits of the estimate

Heat content depends on moisture. Wood that has not dried for months or a year burns poorly and wastes energy boiling off water. The USU numbers are for dry wood. Loose piles, bark, crooked splits and thick air gaps also reduce the actual wood in 128 cubic feet.

  • Species: six are listed; mixed loads should be averaged by hand.
  • Safety: burn only seasoned wood in a properly installed and inspected stove or fireplace.
  • Prices: electricity, propane and gas inputs are optional and are never filled in for you.

Sources and next steps

Utah State University Extension, 'Wood Heating,' Table 1 and the Firewood Volume section (extension.usu.edu/forestry/resources/forest-products/wood-heating). U.S. Energy Information Administration, 'Energy units and calculators explained' for BTU per kWh, gallon of propane and cubic foot of natural gas.

Next, use the heating load calculator to see how much heat your home needs, the kWh cost calculator for electric heating, and the kWh to BTU converter if you want to check the unit math.

Frequently Asked Questions

Common questions about the Firewood Cord Calculator (Stack Size, Price & Heat Value)

A full cord is a stack 4 ft high, 4 ft deep and 8 ft long, which is 128 cubic feet of stacked wood including the air gaps between pieces. Utah State University Extension uses this definition in its wood heating guidance. Many U.S. states define the cord the same way in law. This tool divides your stack volume by 128 to get cords.

Sources & References

International System of Units (SI): energy, work and heat

Energy, work and heat is measured in the joule (J); 1 cal = 4.184 J. Conversions between SI and other units use exact, internationally agreed factors maintained by NIST.
→Source: NIST — International System of Units (SI)

International System of Units (SI)

Authoritative definitions for energy, work and heat, from the BIPM SI Brochure (9th edition), the defining reference for the SI.
→Source: BIPM — SI Brochure (9th ed.)

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